Simultaneous Screening and Determination of Eight Tetracycline Antibiotics Illegally Adulterated in Herbal Preparations Using HPLC–DAD Combined with LC–MS–MS

In this study, the applicability of high-performance liquid chromatography with diode-array detection (HPLC–DAD) combined with electrospray ionization tandem mass spectrometry (ESI–MS) for the simultaneous screening and determination of tetracycline antibiotic analogues illegally adulterated in herbal preparations was investigated. The HPLC–DAD method could be employed to separate and simultaneously determine eight tetracyclines using an isocratic solvent system. These tetracycline antibiotics include doxycycline, 6-epidoxycycline and tetracycline, which are difficult to identify because they are structural isomers. ESI–MS was used in combination with HPLC–DAD to improve the qualitative accuracy in this study. Method validation included the investigation of linearity, selectivity, stability, limits of detection and quantitation, trueness, precision and ruggedness. The response exhibited a good linear relationship with the analyte concentration. The coefficient of determination (r 2) was greater than 0.9993. The limits of quantification for the examined tetracycline antibiotics ranged from 1.11 to 25.73 µg·mL−1, and the recoveries ranged from 91.0 to 104.0%. The proposed methods were specific, sensitive and accurate, and they could be promising and powerful tools for the routine screening of tetracycline analogues in herbal medicines to ensure food safety and public health.